Water Alarm

I purchased two of these from Lowes.

http://www.lowes.com/SearchCatalogDisplay?storeId=10151&langId=-1&catalogId=10051&N=0&newSearch=true&Ntt=water+alarm

Saw an article in one of my magazines, Detached the sensor head, drilled a hole in the plastic sensor, screwed it to a sponge then to the floor. About $12. One by the water heater and one will be under the bed. They have a long enough wire to detach the unit from the sensor so you can replace the battery if necessary. Any of this make since????